The present invention relates to an optical disk apparatus for reading out information stored on a disk using a light beam, and also relates to a computer with the optical disk apparatus built in.
In recent years, optical disks of various types have been used widely as information storage media for computers and audiovisual (AV) appliances. These optical disks currently available are roughly classified into the two types: read-only optical disks and writable optical disks.
In this specification, a "read-only optical disk" means an optical disk such as CD-ROM and DVD-ROM with information stored as pits (physically concave or convex portions) on the information recording plane thereof. On the other hand, "writable optical disks" include both write-once optical disks such as CD-R and DVD-R, on which information can be written only once, and optical disks such as CD-RAM and DVD-RAM, on which information can be repeatedly written numerous times. In this specification, optical disks of the former write-once type will be called "recordable optical disks", while optical disks of the latter type will be called "RAM optical disks". A recordable optical disk includes a recording layer made of an organic dye material, which absorbs light at a predetermined wavelength to cause an irreversible structural change. In contrast, a RAM optical disk includes a recording layer made of a material, which causes a reversible phase change responsive to incident light thereon.
The recording density and the prescribed wavelength of light applicable to reading and writing (hereinafter, simply referred to as a "reading/writing wavelength") differ depending on the type of an optical disk. For example, the track pitch of a CD including CD-ROM, CD-R and CD-RAM is 1.6 .mu.m, while that of a DVD including DVD-ROM, DVD-R and DVD-RAM with a higher recording density and a larger capacity than those of a CD is 0.74 .mu.m. The reading/writing wavelength of a CD is 780 nm, while that of a DVD is 650 nm. Also, DVD-ROM's are further classified into a single-layered type with only one information recording layer and dual-layered type with two information recording layers. In order to further increase a recording density, optical disks, which are writable and readable with laser light on the blue region of the spectrum, have been developed by utilizing a second harmonic generation (SHG) phenomenon.
Since a wide variety of optical disks are currently used widely, an optical disk apparatus that can read out information from, or is compatible with, any of these various types of optical disks is now in high demand. For example, Japanese Laid-Open Publication No. 9-312057 (corresponding to U.S. Pat. No. 5,831,952) discloses an optical disk apparatus with a function of recognizing the type of a disk loaded as a CD-ROM or DVD-ROM. In this specification, Japanese Laid-Open Publication No. 9-312057 and its corresponding U.S. Pat. No. 5,831,952 are hereby incorporated by reference to illustrate the type recognition of optical disks and the basic structure and operation of the optical disk apparatus of the present invention.
The optical disk apparatus disclosed in the patent identified above can recognize the type of an optical disk loaded and read out information from either a CD-ROM or a DVD-ROM. But the optical disk apparatus, including a laser diode oscillating at a wavelength of 670 nm, cannot read out information from a CD-R. When the apparatus recognizes the type of an optical disk loaded as CD-R, then the loaded optical disk is ejected to prevent the information recorded on the CD-R from being damaged. That is to say, this conventional optical disk apparatus is intended just to read out information from read-only optical disks of various types, not to read or write information from/to writable optical disks.